Pelletization of CaO-based sorbents for CO₂ capture

The use of pelletization technology has been explored for CO₂ capture using Ca looping cycles. The initial work suggests that, whereas binders like Na₂CO₃, and Na and Ca bentonites do make potentially strong pellets, this benefit is compromised by the loss of CO₂ capture activity that results from the presence of elevated levels of Na and/or Si in the binder, even over tens of cycles. This suggests that, if sorbents need to perform for a hundred cycles of more, these materials must be avoided. The use of water sprays to bind pellets is also problematic given that the pellets often lack mechanical strength, and/or tend to be destroyed in the curing process. Experimental work at Canmet Energy suggests that these problems appear to be resolvable by using Ca aluminate cements at about 10% addition level, which give pellets that are strong and show high activity over up to 50-60 cycles. Moreover, such binders are relatively cheap, and our results support the hypothesis that the goal of producing a sorbent capable of achieving avoided CO₂ costs of less than $20/tonne may be achievable using such binders.